Dear CCL users,I received this clear answer from Dr. Philip to my question about the D- and L-Arabinose. Dr. Philip sent me an attached file with the clear answer. I thought It is worthy to pose his answer to the netters.
Many thanks to Dr.Philip. Regards, Ibrahim
From: "Phil Hultin" <hultin<<at>>cc.UManitoba.CA>
To: "Ibrahim M.Moustafa"
<im17<<at>>st-andrews.ac.uk>
Subject: RE: Arabinose structure
Date: Mon, 18 Aug 2003 09:53:33 -0500
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The representation of enantiomeric pyranoses has one thing that confuses a
lot of people. The enantiomer of 4C1-D-arabinose is NOT 4C1-L-arabinose, it
is 1C4-L-arabinose. The mirror imaging affects the conformation as well as
the configuration. You actually cannot refer to the conformational terms
"4C1" or "1C4" without specifying whether you are in the D-
or L-series,
although by convention it is assumed that you are always talking about the
D-series unless otherwise specified. This is why the confusion arises.
Notice that you do NOT flip the axial/equatorial relationships in drawing
the enantiomer. This makes sense - since the enantiomers have identical
chemical and physical properties they must also have identical
conformational free energies. If you changed the conformational
orientations, this would not necessarily be the case, would it?
See the attached GIF image for pictures.
Dr. Philip G. Hultin
Associate Department Head and
Associate Professor of Chemistry
University of Manitoba
Winnipeg, MB, Canada R3T 2N2
(vox) 204-474-9814
(fax) 204-474-7608
mailto:hultin<<at>>cc.umanitoba.ca
http://www.umanitoba.ca/chemistry/
-----Original Message-----
From: Computational Chemistry List [mailto:chemistry-request<<at>>ccl.net]On
Behalf Of Ibrahim M.Moustafa
Sent: August 12, 2003 11:01 AM
To: chemistry<<at>>ccl.net
Subject: CCL:Arabinose structure
Dear CCL users,
I have a small question about the stereochemistry representations of
the pyranoside structure of Arabinose.
How to draw the chair conformation of the D- and L-forms of Arabinose?.
I'm a bit confused; if I want to draw the pyranoside chair
conformation (4C1) of the D-form from the Fischer projection in which the
OH at C2 lies to the left, C3(OH) to the right and C4(OH) to the right, I'd
draw this chair conformation with:
OH(ax) above the ring at C2, OH(ax) below the ring at C3, and OH(eq)
below the ring at C4. Now, If I want to draw the same conformation for the
L-form (the mirror image of D-form), do I need to alternate the OH groups
> from axial to equatorial and vice versa? or how to draw the chair
conformation for the L-form?
I apologize for bothering you with this small question? I could not find
a straight answer for my question in the textbooks of carbohydrate
chemistry.
Appreciated your help.
regards,
Ibrahim
Ibrahim M.Moustafa
Centre for Biomolecular Sciences
St-Andrews University
North Haugh, St-Andrews
Fife KY16 9ST
Scotland, U.K.
Tel. +44 (0)1334 467257
Fax +44 (0)1334 462595
e-mail: im17<<at>>st-andrews.ac.uk
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Ibrahim M.Moustafa Centre for Biomolecular Sciences St-Andrews University North Haugh, St-Andrews Fife KY16 9ST Scotland, U.K. Tel. +44 (0)1334 467257 Fax +44 (0)1334 462595 e-mail: im17<<at>>st-andrews.ac.uk
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